It may be necessary to restrict access to the top of a tubular duct (such as a ladder cage or an inspection duct leading to an underground installation) to authorized persons only because the duct may lead to a security zone or to dangerous materials. Access must therefore be barred by a device which can be operated only by persons possessing the means for unlocking it. However, such barring should not hinder the passage of any user coming up the duct as an emergency exit.
Devices exist for performing this function which comprise a trapdoor-type of flap hinged about a horizontal axis. The main drawback of such devices lies in the fact that the hinged flap may pivot under its own weight from its closed position to its open position if it opens downwardly or from its open position to its closed position if it opens upwardly. This may give rise to accidents due to a slip while opening the flap or due to the flap being improperly latched when in its open position, with the moving panel then striking the person occupying the volume through which it moves (on the head or the hands).
In addition, when a ladder exceeds a certain height, it is necessary to provide landing places, i.e. platforms where the user can stand and let go the ladder in order to take a rest. Conventionally, such rest landing places are constituted by horizontal gangways which serve to interconnect two successive lengths of ladder which are horizontally offset from each other, such that the user is constrained to make use of the gangway both when going up and when going down the ladder. This type of construction is more expensive than a straight ladder and requires additional volume for its installation because of the offset between the lengths of ladder.
The present invention proposes a device for closing a tubular duct which is designed to bar access thereto in a way which avoids the drawbacks of a hinged flap and which also serves to constitute a rest landing place which avoids the need for constructing ladders in offset lengths.